Environment

Ubuntu 16.04 is installed on WSL.
Vivado 2018.3 WebPack is installed both on Windows and WSL Ubuntu 16.04 to default paths.

Maybe it can be done only with WSL Ubuntu 16.04 . (But my vcXsrv often freezes with GUI applications.)

Working path

Windows 10 d:\xlnx

WSL Ubuntu 16.04 /mnt/d/xlnx

Install Digilent board files into Vivado

$ sudo apt install git
$ git clone https://github.com/Digilent/vivado-boards

Then copy ./vivado-boards/new/board_files/* to C:\Xilinx\Vivado\2018.3\data\boards\board_files (See 'Digilent board file installation guide')

Create a CPU design for Zybo Z7-20 (Vivado)

Invoke Vivado on Windows 10.

Select File->Project->New
Click "Next" and "Next", setting:
- Project Name : zybo_z7_20_linux
- Project Path : d:/xlnx
- Board : Zybo Z7-20
Create Block Design
- Design Name: cpu
Click + in diaglam window
Select ZYNQ7 Processing System
Run Block Automation and click OK
Connect FCLK_CLK0 to M_AXI_GP0_ACLK
Create HDL wrapper (A pop-up menu appears with right click on cpu in Sources window.), click OK.
Click Generate Bitstream
Select File->Export->Hardware, check Include bitstream, click OK

Setting environmet variables

Create following env.sh

env.sh

#!/bin/sh

export CROSS_COMPILE=arm-linux-gnueabihf-
export ARCH=arm
export KBUILD_DIR=/mnt/d/xlnx/linux-xlnx-xilinx-v2018.3
export PATH=$PATH:/mnt/d/xlnx/u-boot-xlnx/tools
source /tools/Xilinx/Vivado/2018.3/settings64.sh

Apply it.

$ source env.sh

Build Xilinx u-boot

Because u-boot-xlnx v2018.3 does not have Zybo Z7-20 configuration, need to clone snapshot

$ git clone https://github.com/Xilinx/u-boot-xlnx

The hash of the commit was,

$ git rev-parse HEAD
195c620e348891ca2d90c759781413f2adb3f748

Append the following line to u-boot-xlnx/configs/zynq_zybo_z7_defconfig

CONFIG_OF_EMBED=y
CONFIG_CMD_NET=n

CONFIG_OF_EMBED=y embeds device tree for the board into binary. CONFIG_CMD_NET=n prevents BOOTP tries few times before bootm runs.
If the system does not have flex and bison,

$ sudo apt install flex bison

Build u-boot.

$ cd u-boot-xlnx
$ make zynq_zybo_z7_defconfig
$ make
$ cd ..

Build Xilinx Linux kernel

$ wget https://github.com/Xilinx/linux-xlnx/archive/xilinx-v2018.3.tar.gz
$ tar zxvf xilinx-v2018.3.tar.gz
$ rm xilinx-v2018.3.tar.gz
$ cd linux-xilinx-v2018.3
$ make ARCH=arm xilinx_zynq_defconfig
$ make ARCH=arm UIMAGE_LOADADDR=0x8000 uImage
$ cd ..

Build DTC

$ git clone https://git.kernel.org/pub/scm/utils/dtc/dtc.git
$ cd dtc
$ make
$ cp dtc ../u-boot-xlnx/tools
$ cd ..

Create RAM disk image (see Xilinx wiki)

Download arm_ramdisk.image.gz to /mnt/d/xlnx (d:/xlnx) from here. Then create RAM disk image.

mkimage -A arm -T ramdisk -C gzip -d arm_ramdisk.image.gz uramdisk.image.gz

Because WSL Ubuntu does not have loop device, we cannot mount the root file system as in Xilinx wiki. To modify the image, other Linux computer should be prepared on VMs or PCs.

My own modification on rootfs

Eliminating two lines of fstab mounting SD card to /mnt : I do not know the exact reason why the two lines do not work properly. (/dev/mmcblk0p1 may not be prepared when the auto-mount is invoked.)
Inserting 'mount /dev/mmcblk0p1 /mnt' into /etc/init.d/rcS just before executing /mnt/init.sh.: init.sh placed at root of the SD card is automatically executed at the end of rcS. So init.sh is a convenient mean for us to insert start-up operation without modifying rootfs.

Create FSBL and Device Tree Blob (XSDK on WSL Ubuntu 16.04)

First, download device tree files.

$ wget https://github.com/Xilinx/device-tree-xlnx/archive/xilinx-v2018.3.tar.gz
$ tar zxvf xilinx-v2018.3.tar.gz
$ rm xilinx-v2018.3.tar.gz

Invoke XSDK.

$ xsdk &

Create hardware platform specification

Set workspace directory as /mnt/d/xlnx
Select File->New->Project, select Xilinx->'Hardware Platform Specification', click Next
Set project name to zybo_z7_20_linux_hw, set Target Hardware Specification to /mnt/d/xlnx/zybo_z7_20_linux/zybo_z7_20_linux.sdk/cpu_wrapper.hdf, click Finish

Create FSBL

Select File->New->Application Project, set project name to zybo_z7_20_linux_fsbl
Confirm zybo_z7_20_linux_hw is selected as Hardware Platform
Click Next, Select Zynq FSBL, click Finish

Create devicetree

Select Xilinx->Repositories, select /mnt/d/xlnx/device-tree-xlnx-xilinx-v2018.3 in Global Repositories, click Rescan Repositories, Apply, then OK
Click File > New > Board Support Package, set Project name to zybo_z7_20_linux_dt_0, select 'device_tree' in 'Board Support Package OS', click 'Finish', then 'OK'

Modify and build device tree

At /mnt/d/xlnx/zybo_z7_20_linux_dt_0 (WSL Ubuntu 16.04), revise following lines in system-top.dts

system-top.dts

09 #include "zynq-7000.dtsi"
10 #include "pcw.dtsi"
21         memory {

system-top.dts(revised)

09 /include/ "zynq-7000.dtsi"
10 /include/ "pcw.dtsi"
21         memory@0 {

Insert the description of Ethernet PHY into &gem0 node in system.dts

system.dts

&gem0 {
    local-mac-address = [00 0a 35 00 00 00];
    phy-handle = <&ethernet_phy>;
    ethernet_phy: ethernet-phy@0 {
              reg = <0>;
    };
};

Compile device tree as,

dtc -I dts -O dtb -o devicetree.dtb system-top.dts

Create boot image

At /mnt/d/xlnx (WSL Ubuntu 16.04),

$ mkdir zybo_z7_20_linux_boot
$ cd zybo_z7_20_linux_boot
$ cp ../zybo_z7_20_linux_hw/cpu_wrapper.bit fpga.bit
$ cp ../zybo_z7_20_linux_fsbl/Debug/zybo_z7_20_linux_fsbl.elf fsbl.elf
$ cp ../u-boot-xlnx/u-boot u-boot.elf
$ cp ../linux-xlnx-xilinx-v2018.3/arch/arm/boot/uImage uImage
$ cp ../uramdisk.image.gz uramdisk.image.gz
$ cp ../zybo_z7_20_linux_dt_0/devicetree.dtb devicetree.dtb

Create boot.bif as

boot.bif

image : {
      [bootloader]fsbl.elf
      fpga.bit
      u-boot.elf
}

Run bootgen

bootgen -image boot.bif -o i boot.bin

Boot

Move follwing files to a SD card.
- boot.bin
- devicetree.dtb
- uramdisk.image.gz
- uImage

Insert SD card to the slot.
Confirm 'JP5' is in SD boot configuration.
Connect USB cable to PROG/UART port
Slide power switch and open the serial terminal with 115200 bps.

Appendix

Kernel configuration

First, install ncurses-dev if the system does not have.
$ sudo apt install ncurses-dev
Then, execute following at the root of the kernel source.
$ make ARCH=arm menuconfig

Creating Xilinx Linux SD boot image for Zybo Z7-20 on Windows10 (Ubuntu16.04 WSL)